The Wittig Synthesis. I. Use of Certain Aliphatic Aldehydes As

Charles F. Hauser, Thomas W. Brooks, Marion L. Miles, Maurice A. Raymond, and George B. Butler. J. Org. Chem. , 1963, 28 (2) .... Gebreyes , John. Hut...
0 downloads 0 Views 1MB Size
Download PDF
HAIJSER, BROOKS, MTT,RS, RAYMOND, .\m BUTLER

372

VOL. 28

The Wittig Synthesis. I. Use of Certain Aliphatic Aldehydes As Intermediates in the Synthesis of Olefins' CHsRLES F. HAUSER, THOMAS \y.

1,. MILES,n I A U R I C E A. RAYMOND, GEORGE B. BUTLER

BROOKS, R I A R I O N

AND

Department of Chemistry, University of Florida, Gainesville, Florida Received July I d , 1962 The Wittig method of olefin synthesis has been extended to include aliphatic aldehydes as the carbonyl function. Both gaseous and paraformaldehyde, acetaldehyde, propionaldehyde, n- and isobutyraldehyde, n-hexaldehyde, 4-pentenal, acrolein, and methacrolein have been utilized for preparation of a number of olefins containing ethylene, butadienyl and isoprenyl linkages. It is shown that these reactions tend to be quite rapid and may be carried out under very mild thermal conditions by use of aqueous quenching solutions. The cis isomer predominated in the preparation of both 2-octene and 4-octene. Qualitative evidence has been obtained for a halogen anion effect upon the rate of condensation of formaldehyde with bensylidenetriphenylphosphorane (11. R1 = H; R Z = -CsHs). Two diterminal olefins have been prepared by condensation of the appropriate biphosphoranes with formaldehyde.

Although more than one hundred and fifty articles2 relating t o olefin synthesis via the "Wittig" reaction (equation 1) have appeared in the literature since the

a competing reaction in the case of such aldehydes, as appears t o be the case with the more strongly basic phosphoranes. The Wittig reaction has also seen extensive use in the n-BuLi preparation of compounds possessing exocyclic methyl(CeH6)aP+--CHRiR&- -+ Ether ene groups via condensation of methylidenetriphenylI (C6H6)3P-CRlR2 + LiX ( l a ) phosphorane (11. R1 = Rz = H) with carbonyl-containing compounds. However, no investigation has yet been conducted with regard to the syntheses of this (CsH5)3P=CRiRz type of olefin by the converse of the above reaction I1 ( X - = C1- or Br-) sequence; that is, by condensation of various phosphoranes (11. R1 and Rz = H, aliphatic or aromatic) with I1 RaR4CO +RiRzC-P( C6Hs)z I formaldehyde as the carbonyl-containing species. ~ ~ ~ -~ 6 - 0 (1b) Organic halides are, on occasion, more readily accessible I11 than are the corresponding carbonyl derivat,ives. RIR~C-P(CBH~)~ + RIR~C=CR~RI(V) + (IC) Therefore, facile substitution of a methylene group a t 111 + the position of the halogen atom in such halides would RaR4C(CeH&P +0 enhance the versatility of the Wittig method as a synIV thetic tool. initial paper by Wittig and Schollkopf3 in 1954, the It is not readily apparent whether this absence of synthesis of olefins by this method employing simple literature reports on use of such carbonyl compounds as aliphatic aldehydes and more reactive aldehydes such as intermediates in the Wittig synthesis is due to failure of acrolein has remained essentially untouched. Bohlthese compounds to function normally, or to the fact mann and Mannhardt4 reported less than 1% yield of that such experiments have not been carried out. the polyene derived from reaction of acrolein with the Efforts in these laboratories to utilize such reactive ylide produced from 2,8-decadiene-4,6-diyneyltriphenyl- aldehydes employing the normal conditions failed. phosphonium bromide. During the course of this work, Procedures involving long reflux periods (24 hours) in Trippett and Walker5 reported on the reaction of pure ethylene glycol dimethyl ether and in ether were unsucphosphobetaines, (C6H5)3P= CHR, in which R = cessful when the reactants were (1) the ylide from 5COSHz or -CHO, with n-heptaldehyde and 2,7-dihexenyltriphenylphosphonium bromide and acrolein methyl-2,6-octadiene-4-ynedial, an a,@-unsaturated and (2) the ylide from allyltriphenylphosphonium dialdehyde. However, these phosphobetaines, isolated bromide and 5-hexenal. Similar experiments using the as pure crystalline compounds, are stable to hydroxylic ylide from allyltriphenylphosphonium bromide and nsolvents a t room temperature, indicating their weakly butyraldehyde were also unsuccessful. basic character. Such weakly basic compounds would This was tentatively attributed to the pronounced not be expected to catalyze aldol-type condensations as tendency for aldehydes containing one or more alphahydrogen atoms to undergo aldol and related reactions (1) (a) This work was supported b y the Kational Science Foundation, g r a n t no. NSF-G-10011. by the Petroleum Research Fund, American in the presence of strong bases such as butyl lithium, Chemical Society ( P R F grant 470-A), and by the Aeronautical Systems which was used in excess to generate the phosphorus Division, U.S. Air Force, urlder contract no. AF 33(616)-6887; (b) C. F. ylide, or even the ylide itself. It is also known that Hauser a n d G. B. Butler, Abstracts of Combined Southwest-Southeast Regional Meeting, New Orleans, Lit., December 7-9, 1961, p. 411. C. F. a,@-unsaturatedaldehydes, such as acrolein, are subHauser, M. L. Miles. and 0.B. Butler, Abstracts of Papers, Division of ject to extensive polymerization in presence of such Organic Chemistry, 142nd National Meeting of the American Chemical strong bases. These facts could account for the essenSociety, Atlantic City, N. J., September 9-14, 1962, p. 59Q. (2) -J. LeVidles. Bull. 8OC. chin. Prance. 1021 11958); (b) u. Schdllkopf, tial absenceof reported use of these compounds in this Anpew. Chem., 71, 260 (1959); ( 0 ) R. C. Slagel, Illinois Seminar, November synthesis. The possibilities that, formation of the 17, 1960, pp. 92-101; (d) S. Trippett, "Advances in Organic Chemietry," Vol. I , Interscience Publishers, Inc., Kew York, K. Y., 1960, pp. 83-102. reactive complex (111) constitutes a very rapid step, (3) G. Wittig a n d U. Schollkopf, Ber., 87, 1318 (1954). and that immediate quenching, resulting in collapse of (4) F. Bohlmann and H. J. Mannhardt. ibid., 88, 1330 (1955). this intermediate to the olefin and triphenylphosphine ( 5 ) 8. Trippett and D. M. Walker, J . Chem.. B n c . . 1206, 2130 (1901).

!

+

'A

373 TABLE 1" ALDEHTDER, ACROLEINAKD

OLEFINS SYUTHESIZED FROM SIMPLE .kLIPHATIC

i\lETHACROLEIN

Reaction

Yield, Phoaphorane (11)

Olefin

no.

70

Aldehyde

B.p.

69 124-125" Ri = H ; Rz -(CHz)dCHj CHaCHO RI = H ; Rz = (CHz)zCH3 CH3(CHz)zCHO 82 121-122' Ri = H ; Rz = (CHa)zCH3 CHaCH(CH8)CHO 67 110-111' Ri = CHa; R? = -CHICHI CHs(CH2)zCHO 68 120-121' 5 Ri = H ; Rs = -ceH5 CHICH~CHO Z3 92-93"/23 mm Oh Ri = H ; Rz = -CH=CHz CHa(CH2)zCHO 28 (52) 99-100' Gn Ri = H ; R2 = -( CH2)rCHs CH?=CHCHO 34 70-71'/44 mm. ib Ri H ; Rz -CH=CHa CHa(CH2)4CHO 30 70-71°/44 mm. CH.=C( CHa)CHO 38 74-77"/25 mm. Sa CH,=C(CH,)-CH=CH(CH,)4CH$ Ri = H Rz = -(CHz)&Hs 8b Ri = H ; Rz = -C(CHa)=CH? CHs(CHz)aCHO 14 74-77"/25 mm. 9a CH2=CH-CH=CH-( CH2)zCH=CH2 R1 = H ; R2 = -(CHz)zCH=CHz CHz=CHCHO 24 124-125" R1 = H ; Rz = -CH=CHz CH2=CH-(CHa)aCHO 12 124-125" 9b 10 CHa=CH-CH=CH-(CH%)aCH=CHa R1 H ; RZ -(CH2)3CH=CHz CHa=CHCHO 17 68-69"/43 mm. 11 CHa=CH-CH=CHCH&H= ( CsHo)3P=CHCH?CH=P( C ~ H S ) ~CH,=CHCHO 6 (12) 52 O / 2 0 mm. CH-CHzCH, 12' CHj=CH-CH-CH( CH?)jCH= (CsH,)sP=CH( CHa)sCH=P( C6H5)3 CHa=CH-CHO B(12) 71-73"/2 mm. CH-CH=CHa Phosphorane derived from the allylphosphonium bromide afforded olefin in 28% yield; phosphorane a Boiling ranges uncorrected. derived from phosphonium chloride afforded olefin in 52% yield. Tetraene isolated in 6% yield with diethyl ether solvent; 12cJ, yield with diglyme as solvent. 1 2 :3 4

CHICH=CH( CH2)rCHa CHs(CHz)*CH=CH( CHz)aCH3 CH,CH( CHa)CH=CH( CH*)zCH3 CH&HzC(CH,y)=CH(CH2)&Hs CeH,CH=CHCH?CHa CH:=CH-CH==CH(CHa)aCH, CHz=CH-CH==CH( CH3)ICHa

TABLE IIa OLEFINSSYNTHESIZED FROM GASEOUS FORMALDEHYDE OR PARAFORMALDEHYDE Reaction no.

Olefin (IV)

Phosphorane (11)

Aldehyde

Yield,

B.p.

1 CHZ=CH( CHz)4CHa Ri = H ; Rz = -(CHz)4CH3 CHzO 47 93-94" 121-122" ( CHaO In 42 2 CHz=CH(CHz)sCHa Ri = H ; Rz = -(CHa)aCH3 CHaO 64 52-53'/27 mm. 3a C6HsCH=CHza Ri = H ; Rz = -CeHs ( CHz0 LL 65 52-53"/27 mm. 3b C6HsCH=CHzb Ri = H ; R2 = - C a s (CHzOh 75 52-53"/27 mm. 3c C6HjCH=CHzC Ri = H ; Rz = -CBHs 4 CH?=C( CHs)(CHz)6CH3 Ri = CH3; Rz = -(CHz)sCHa ( CHzO )n 52 142-143' a Boiling ranges are uncorrected; yields based upon gas-liquid chromatography analysis of distillation fractions over a somewhat Phosphorane prepared from benzyltriphenylphosphonium bromide. Phosphorane prepared from wider range than recorded. - benzyltrip6enylphosphonium chloride:

oxide, could overcome the difficulty postulated above, lead to the work reported here. Following this approach, it has been found that this method of olefin synthesis can readily be extended to include aldehyde types such as formaldehyde, either gaseous or paraformaldehyde, n-butyraldehyde, acrolein and methacrolein for the preparation of a large number of olefins containing ethylene, butadienyl, and isoprenyl linkages. Moreover, these olefins may be prepared under considerably milder reaction conditions than those normally employed in Wittig syntheses. A number of mono- and polyolefins have been prepared by use of these types of aldehydes, the results of which are presented in Table I. The olefins possessing only one double bond were generally isolated in good yields, ranging from a high of 82y0of theoretical for 4octene (2) to a low of 67% for 2-methyl-3-heptene (3). In contrast, however, the yields of polyenes were somewhat lower, varying from a low of 6% of theoretical for l13,6,8-nonatetraene and 1,3,9,1l-dodecatetraene (11 and 12, respectively) to a high of 52% for 1,3-heptadiene (6). These yields, although somewhat less than may be desired, are nevertheless quite satisfactory in consideration that the majority of these polyenes are a t best only difficultly accessible by other means. Indeed, it is ent,irely possible that, the mild thermal conditions em-

ployed for the olefins shown in Table I allowed the isolation of the two tetraenes (11 and 12, respectively). Two supplements to the data presented in Table I should be mentioned. First, the yield of 1,3-heptadiene appeared to be directly dependent upon the kind of halide ion (chloride us. bromide) associated with the phosphonium halide salt from which allylidenetriphenylphosphorane (11. R1 = H, R2 = -CH===CH2) was derived (6). I n particular, the phosphorane derived from allyltriphenylphosphonium chloride afforded the diene in 52% yield, whereas only a 28% yield was obtained when the phosphorane was derived from allyltriphenylphosphonium bromide. Second, the reported yields of olefins were obtained via condensation of two equivalents of aldehyde with one equivalent of phosphorane. Better yields seem to have resulted from a 2 : 1 ratio of aldehyde to phosphorane than were obtained from a 1: 1 ratio. Four olefins possessing a single terminal methylene group have subsequently been prepared from readily accessible organic halides and formaldehyde. The results of these preparations are presented in Table 11. Reasonably good yields of olefin products were obtained, ranging from a high of 757& of theoretical for styrene, (3c) to a low of 42y0 for l-octene (2). The use of paraformaldehyde, us. gaseous formaldehyde, appeared to

HAUSWR, BROOKS, RfILES, RAYMOND, AND BUTLER

374

have little adverse effect upon the yields of olefins but offered the advantage of a more simplified experimental procedv re. Sonic very interesting observations have arisen from the above work. Of particular interest was the observation that the kind of halogen anion (chloride or bromide) present in the benzyltriphenylphosphonium compounds (I. R1 = H, RO= -C6H5) from which benzylidenetriphenylphosphorane (11. R1 = H, Rz = -CBH6) was derived appeared to play a significant role in the rate with which I1 (R1 = H, Rn = -CaH6) reacted with formaldehyde. Indeed, a qualitative study (Table 111) of the rates with which paraformaldehyde TABLE IIIa

Reaction no.

Phosphonium halide

CHLORIDE us. BROMIDE Decolorization time, min.

28

arisen by way of greater resonance stability offered by the benzal moiety during the bentaine formation step than could be offered by the alkyl moieties. Attention, thus far, has been given only to the addition of a single formaldehyde moiety to certain monophosphoranes (11). However, it has now been shown that two formaldehyde units may be added to biphosphoranes of the types VI and VII, by a procedure analogous to that described earlier3 for the addition of acrolein to similar biphosphoranes, to afford a convenient route to the corresponding symmetrical dienes. (CsHs)3PzCH (CH2)nCH=P(C&,) 3 VI

( c ~ H ~ ) ~ P = cHQcI-I=~(~~H,~,

QUALITATIVERATE STUDIESOF BETAINEFORMATION AS A FUNCTION OF THE PHOSPHORANES DERIVED FROM BENZYLTRIPHENYLPHOSPHONIUM

VOL.

Styrene yield, '%*

Bromide 390 78 Bromide 270 82 Bromide 330 75 4 Chloride 27 79 5 Chloride 32 82 6 Chloride 28 80 a All reactions conducted a t 34'; phosphorane concentration of 0.17 M (0.02 mole in a tctal of 100 ml. of anhydrous ether and 18 ml. of anhydrous hexane). Styrene yields determined by gas-liquid chromatography analysis. 1 2 3

decolorized ethereal suspensions of the phosphorane derived from benzyltriphenylphosphonium chloride (A) us. those derived from benzyltriphenylphosphonium bromide (B) revealed (A) to be an order of magnitude faster than (B). At a concentration of phosphorane of 0.17 M and a temperature of 34', the average time required for decolorization of (A) was found to be thirty minutes, whereas the average time required for decolorization af (B) was three hundred and thirty minutes. These two reaction series, which were conduated under similar conditions, apparently differed from one another only in the type of halogen anion (chloride us. bromide) associated with each of the subject benzyltriphenylphosphonium salts. It would seem, therefore, that some sort of halogen anion effect is operative in these cases. Another interesting observation arising from the work presented in Table I1 is the difference in rates of decolorization by formaldehyde, either gaseous or paraformaldehyde, of ethereal suspensions of the two n-alkylidinetriphenylphosphoranes US. the rate of decolorization of ethereal suspensions of benzylidenetriphenylphosphorane. Paraformaldehyde appeared to decolorize suspensions of benzylidenetriphenylphosphorane (3b) several times more rapidly than it decolorized suspensions of n. heptylidenetriphenylphosphorane (2). Moreover, suspensions of the former phosphorane seemed to have been decolorized several times more rapidly by gaseous formaldehyde (3a) than those of n-hexylidenetriphenylphosphorane (1). It may have been expected that the powerful carbanions of the n-alkylidenephosphoranes would have reacted more rapidly with formaldehyde to form betaine structures than would have the relatively weak carbanion of the benzylidenephosphorane. The observed order of reaction, contrary to this expectation, may have

VI1

The two diterminal olefins, 1,6-heptadiene and p divinylbenzene, were obtained in reasonable yields of 45% and 42%, respectively. Although l,&heptadiene was synthesized by way of gaseous formaldehyde and p divinylbenzene by way of paraformaldehyde, it is conceivable that similar results would be obtained upon reversal of the respective modes of addition of formaldehyde to the two biphosphoranes. These results are recorded in Table IV. The mechanism of the Wittig olefin synthesis has been proposed3 as one involving a nucleophilic attack of a phosphorane (11) upon the carbonyl carbon of an aldehyde or ketone [equation lb) with formation of a zwitterionic intermediate or betaine (111). The betaine could thus be decomposed, via a four-membered cyclic intermediate (IV), by heat or prolonged standing a t room temperature with subsequent splitting out of triphenylphosphine oxide and formation of the olefinic product (V). During the synthesis of each of the olefins presented in Table I, it was observed that, in similarity with some earlier literature reports,6 the intense color of the ethereal phosphorane solution or suspension was discharged immediately upon addition of aldehyde to produce a heavy, cream-colored mixture. This phenomenon was observed even at 10' for all cases (although a t - 10' propionaldehyde required a finite length of time to decolorize a suspension of benzylidenetriphenylphosphorane), which implied a rapid conversion of reactants into betaine-type intermediates (111) or indeed into olefin products and triphenylphosphine oxide. The reaction mixture of n-butylidenetriphenylphosphorane with n-butyraldehyde ( 2 ) has been shown to be approximately two-thirds complete, without quenching, within a condensation period of thirty minutes a t 10'. (See Experimental.) In this example, a t least, the reaction appears to proceed quite swiftly through the intermediate stages to afford the olefin, whereas the intermediate species of certain other condensations may be less prone to undergo rapid decomposition into products. I n any case, however, the decomposition of intermediate species into olefins and triphenylphosphine oxide, or perhaps reverse decomposition into reactants, may be brought about or a t least more rapidly completed for the olefins mentioned in this text by the addition of a quenching solution to the heavy, cream-colored con(6) (a) F. Bohlmann, Ber., 90, 1.519 (1987); (b) G. Wittig and U. Schollkopf, ibid., 87, 1318 (1954).

FEBRUARY, 1963

375

THEWITTIGSYNTHESIS. I TABLE IVa POLYENES SYNTHESIZED FROM FORMALDEHYDE INTERMEDIATE

Polyene

CH?CH(

1

2 a

CHz)aCH=CH*

CHz=CH--&H=CHz

-

Biphosphorane (VI)

Aldehyde

(CeH6)3P=CH( CHz)aCH=P( C&H6)3 ( C e H & P = C H O C H = P ( CBHL)B

Yield, %

B.p.

CHzO

45

89-90'

(CH20)n

42

62-63"/6 mm.

Boiling ranges are uncorrected.

mixtures of the isomeric 4-octene and the authentic cis isomer. Moreover, the isomeric 4-octene exhibited an infrared absorption band of medium strength in the region of 965 cm.-', as contrasted with the very strong band exhibited by the authentic trans isomer a t that frequencys and the relatively weak band exhibited by cis-4-octene. Also, a broad band of moderate strength was observed for the isomeric mixture in the region of 710-690 cm.-', a region normally associated with cis olefins.8 Similar results were obtained for the isomeric 2-octene upon analogous comparison by g.1.c. and infrared analysis with authentic samples7of cis- and trans2-oc t ene. A study of the effects of temperature and condensation time upon the distribution of geometric isomers in 2- and 4-octene has been conducted and the results are presented in Table V. However, with the possible ex-

densation mixtures. The yields of olefins reported in Table I are those obtained by water decomposition of the reaction mixtures following a five-minute condensation period at 10'. I n each instance the addition of water almost immediately transformed the heavy, ethereal mixture into clear water and ether layers (a small amount of amorphous solid usually remained in the water layer) from which the olefin product could easily be isolated. Reaction times considerably in excess of five minutes did not appear detrimental to the yields of olefins derived from the aliphatic aldehydes presented in Table I. However, longer reaction times did appear to decrease the yields of olefins derived from acrolein and methacrolein. In a test case the yield of 4-octene was observed to be dependent upon the nature of the quenching solution. The olefin was produced in 82%, 75% and 55y0 yields upon quenching of the particular reaction mixture with water, in aqueous ammonium chloride solution, and in aqueous hydrochloric acid solution, respectively. The preparation of stilbene (V. R1 = R3 = H,Rz = R4= -c&) uia condensation of benzylidenetriphenylphosphorane (11. R1 = H, Rz = -c6Hs) with benzaldehyde has been reported, after allowing the reaction mixture to stand a t room temperature for two days, to afford the olefin in 82% yield.3 By contrast of conditions, however, a condensation of the same phosphorane with benzaldehyde a t 10' for five minutes followed by decomposition of the reaction mixture with water, afforded stilbene in a similar yield of 78%. The synthesis of olefins by the Wittig reaction has generally been observed to afford mixtures of cis and trans isomers, wherein the trans species tends to be the predominant isomer.2 The general predominance of trans is believedzbto arise by the path. of least steric interference between R groups (See equation 1) in the four-membered cyclic transition state (IV). If, therefore, a l12-disubstituted ethylene (V. R1 = R3 = H, Rz = R4 = aliphatic) were to be synthesized by appropriate choice of phosphorane (11) and aldehyde, the product would be expected to contain a predomjnance of the trans isomer. However, the preparation of both 2-octene and 4octene (Table I, 1 and 2, respectively) afforded a predominance of the cis,not the trans, species. The assignment of geometric structures has been authenticated by comparative gas-liquid chromatography and by infrared analysis of each reaction product with authentic samples' of the appropriate cis and trans isomers. The chromatograms of each olefin exhibited first a smaller and then a larger peak. Mixtures of authentic trans-4-octene with the isomeric 4-octene obtained in Table I resulted in a proportional increase in the area of the f i s t and smaller peak with respect to the second peak. Opposite results were obtained from

ception that lower temperatures tend to lessen the predominance of cis isomer, no conclusive results are to be drawn from the study at this time. The syntheses of two additional alkyl-substituted ethylenes shown in Table I, 2-methyl-3-heptene (3) and 3-methyl-3-heptene (4), may have been brought about with a predominance of the cis isomer. The infrared spectrum of 2-methyl-3-heptene showed a broad absorption band of moderate strength in the region of 740700 cm. and a moderate absorption around 965 cm. -I. An authentic sample' of trans-2-methy1-3-heptenel however, exhibited no similar absorption in the region of 740-700 crn.-l, but showed a very strong absorption band around 965 cm.-'. Analysis of the 2-methyl-3heptene by g.1.c. techniques, however, on a variety of column packings produced in each case only a single, sharp peak, the retention time of which was only slightly different from that of an authentic trans sample. Moreover, essentially no alterations in the shapes of the chromatograms were detected when mixtures of 2-methyl-3heptene and the authentic trans isomer were subjected to similar analysis.

(7) Supplied through the courtesy of Dr. Kenneth W. Greenlee, Director of the Ohio State University Hydrocarbon Laboratory, Columbus, Ohio.

(8) See L. J. Bellsmy, "The Infrared Spectra of Complex Moleculea," 2nd ed., John Wiley and Sons, Ino.. New York, N. Y., 1958. chap. 3.

TABLE V INFLUENCE OF TEMPERATURE AND CONDENSATION TIMEUPON CiS:tTanS ISOMER

Olefin

4-Octene

DISTRIBUTION O F 2-

Temp., 'C.

Time, min.

-15 10

5 5 0.3 5

AND

4-OCTENE &:trans"

Yield, %

ratio

76 67: 33 78 71:29 10 82 84: 16 2-Octene -15 60 77:23 10 A 69 87: 13 0.3 62 81 : 19 10 a Isomer ratio determined by gas-liquid chromatography analysis on a 10-ft., 20% Carbowax 1000 (on 42/60 firebrick) column.

376

HATJSER,

BROOKS, MILES, RAYMOND, AND

The infrared spectrum of the second olefin, 3-methyl3-heptene exhibited very little absorption in the region of 965 cm.-l, contrary to what may have been expected if indeed the olefin contained an appreciable quantity of the trans isomer. Moreover, g.1.c. analysis on several different column packings produced chromacograms in each case possessing a single, but relatively broad peak. It would, therefore, seem that the cis isomers were certainly present in the reaction products of the above two olefins, although in neither case is sufficient data yet available to verify predominance or exclusive presence of either isomer.

Experimental9 2-Octene. A. n-Hexyltriphenylphosphonium Bromide.-A mixture of 458 g. (1.75 moles) of triphenylphosphorus10 and 288 g. (1.75 moles) of n-hexyl bromide in 500 ml. of monochlorobenzene was refluxed with stirring for 24 hr., a t which time the mixture was allowed t o cool and the supernatant liquid poured away from the viscous oil in the bottom of the flask. The oil was mixed with 500 ml. of ether, whereupon the resulting pasty mass solidified after standing for several hours a t room temperature. The solid was triturated several times with ether and dried in vacuo over phosphorus pentoxide to affcrd 666 g. (90% yield of theoreThe n-hexyltritical) of a light tan solid of m.p. 198-200'. phenylphosphonium bromide was stored in a capped bottle in a desiccator. Anal. Calcd. for CsaHssPBr: C, 67.4; H, 6.6; P , 7.3, Found C, 67.3; H , 6.6; P, 7.2. B. 2-Octene.-To a stirred suspension of 42.7 g. (0.1 mole) of n-hexyltriphenylphosphonium bromide in 400 ml. of dry ether under a nitrogen atmosphere was added 90 ml. of 14.90y0 nbutyllithium (0.15 mole) in hexane" by means of a hypodermic syringe and a syringe cap. The resulting deep red solution was coded to 10" in a Dry Ice-acetone bath and a solution of 8.8 g. (0.2 mole) of acetaldehyde in 200 ml. of dry ether was added over a period of 1 min. while maintaining the bath temperature a t 10". A heavy, cream-colored suspension resulted almost immediately which, after stirring for a total of 5 min. a t lo", was decomposed by the addition of 250 ml. of water. The layers were sepaiated and the water layer extracted once with 150 ml. of ether, whereupon the ethereal fractions were combined, dried over anhvdrous sodium sulfate and most of the solvent distilled away after removal of the drying agent. The resulting oil was fractionated through a 28 themetical plate, spinning band distillation column, after which the distillation fractions were analyzed for yield by g.1.c. using a 10-ft., 20% Carbowax 1000 (on 42/60 firebrick) column.12 A second final work-up procedure was sometimes used wherein, after removal of the solvent from the dried ethereal solation, dry petroleum ether (b.p. 30-60') was added to the remaining oil until precipitation ceased. The mixture was allowed to stand for 1 hr., a t which time the supernatant liquid was poured away from the solid material, consisting largely of triphenylphosphine oxide, m.p. 148-152" (lit.,3 m.p. 152.5-154.0"), and most of the petroleum ether removed. The remaining oil was subsequently fractionated through the spinning band column. Similar yields were obtained by either route. 2-Octene, b.p. 124-125' (lit.,13 b.p. cis, 125.6"; trans, 125.0"); n 2 5 1.4092 ~ ( l i t . , 1 3 n 2cis, 5 ~ 1.4139; trans, 1.4128), was obtainedin 69% (7.7 g.) yield of theoretical14 as based upon the n-hexyltriphenylphosphonium bromide. Qualitative g.1.c. analyses12 afforded reasonable separation of the puIe product into two peaks. The area under the first and smaller peak could be increased proportionately with respect to (9) Meltina and boiling ranges are uncorrected. Analyses were b y Galbraith Microanalytical Laboratories, Knoxville, Tenn., and Micro Tech Laboratorieb. Skokie. Ill. (10) Obtained from Peninsdar ChemResearch. Inc., Gainesville. Fla. (11) Foote Mineral Company, Philadelphia 44,Pa. ( 1 2 ) Column obtained from Wilkens Instrument and Research, Inc., Walnut Creek, Calif. (13) "Selected Values of Physical and Thermodynamic Properties of Hydrocarbcns a n d Related Compounds," Carnegie Press, Pittsburgh, Pa., 1953. pp. 58-59. (14) The yield of product was based upon p.1.c. analysis of distillation fractions Over a somewhat aider boiling range than recorded.

VOL. 28

BUTLER

the area under the second peak, or vace versa, by use of mixtures of the pure reaction product with authentic trans-2-octene or authentic cis-2-octene,' respectively. The czs isomer was thus shown to be predominant. The predominance of cis-2-octene was found to vary, depending upon the reaction conditions (see Table V), from a 3: 1 ratio to a 4: 1ratio with respect t o the trans isomer. Infrared absorption bandss were observed for the isomeric 2octene a t 1670, 965 and 690 cm.-l. The band a t 965 cm.+ was of intermediate strength as compared with the very intense absorption exhibited by the trans isomer and very weak absorption exhibited by the cis isomer in this region.8 Moreover, the cis, not the trans isomer, showed absorptions in the region of 690 cm.?. The following nine mono- and polyolefins were prepared by experimental procedures similar t o that used for the preparation of 2-octene with the exception of the types of phosphonium halide salts and aldehydes employed. 4-Octene.-4-Octene, b.p. 121-122' (lit.,13 b.p. czs, 121.7O; ~ (lit.,13n20~ cis, 1.4136; trans, 1.4416), trans, 121.4'); n 2 01.4130 was obtained in 80% yieldla via condensation of the phosphorane derived from n-butyltriphenqlphosphonium bromideI5 with nbutyraldehyde. A similar result, that is a predominance of cis isomer, was found for the 4-octene reaction product as was found previously for 2octene when subjected to g.1.c. and infrared analysis with authentic cis- and trans-4-octene samples.? The predominance of cis isomer with respect t o trans isomer was found to vary from a 2 : 1 ratic to a 4: 1 ratio depending upon reaction conditions (see Table

V).

Attempted Isolation of Intermediate to 4-Octene.-To a stirred solution of n-butylidenetriphenylphosphorane(0.08 mole) in 300 ml. of anhydrous ether, prepared by the previously described procedure, was added a t 10" a solution of 11.8 g. (0.16 mole) of nbutyraldehyde in 20 ml. of dry ether. The resulting creamcolored, heavy suspension was allowed to stir a t 10' for 5 min., a t which time the reaction flask was connected to a vacuum line by way of two Dry Ice-acetone-cooled traps. A pressure of about 15 cm. was applied to the system for 25 min. while holding the temperature a t l o o , a t which time the vacuum was released and the clear liquid in the trap (about 150 ml.) subsequently concentrated to a volume of 40 ml. (phase I). The wet solid remaining in the reaction flask was filtered through a sintered-glass funnel under anhydrous conditions (within 30 min. after initial condensation) and the white solid remaining on the filter washed with dry pentane. The filtrate was poured into a separatory funnel and shaken with 200 ml. of water, whereupon some precipitate appeared but quickly reentered solution. The layers were separated and the water layer extracted once with ether. The ether extracts were combined, dried over anhydrous calcium chloride and most ef the solvent distilled away after removal uf the drying agent (phase 11). The white solid obtained from the above anhydrous filtration was well shaken with a mixture of 150 ml. of water and 50 ml. of pentane and let stand for several hours. The resulting mixture was filtered and washed well with water, followed by pentane. The white solid remaining on the filter was then dried to yield 15.3 g. (69%) of triphenylphosphine oxide of m.p. 147-151' and mixed m.p. 150-153' with authentic sample of m.p. 153" (lit.,3 m.p. 152.5-154.0'). The filtrate was separated into layers and the water layer extracted once with ether. The organic extracts were combined, dried over anhydrous calcium chloride and most of the solvent distilled away after removal of the drying aLent . (phase 111). Phases I. 11. and I11 were fractionated separately in a spinning band column and the distillation fractions analyzed for yield bv g.1.c.l4 Phases I , 11, and I11 contained 2%, 50% and 26% yields, respectively, of 4-octene. 2-Methyl-3-Heptene.-2-Methyl-3-heptene, b .p. 110-1 I1 (lit.,I3 b.p. 112.0"); n 2 0 ~1.4103 (lit.,13 n20~1.407), was obtained in 67% yieldI4 via condensation of the phosphorane derived from n-butyltriphenylphosphonium bromide'5 with isobutyraldehyde. Anal. Calcd. for CsHls: C, 85.62; H , 14.37. Found: C, 85.61; H, 14.43. The moduct exhibited characteristic infrared absorption bands8 a t 1706, 1640,970 and 730 cm.3. G.1.c. analysis,12;sing 5- and 10-ft. Carbowax columns, a 10-ft Carbowax 20 hII column, and a 5-ft. Ucon polar column, showed only a single, sharp peak with no O

(15) R. Mechoulam and F. Sontiheimer, (1958).

J. .4m. Chem.

Soe., 80, 4 3 %

~

THEWITTIGSYNTHESIS.I indication of splitting into cis-trans isomers. Subsequent efforts to separate cis-trans isomers of the straight-chain octenes on a 5-ft. Lcon polar column with 5% added silver nitrate were not succeeaful. 3-Methyl-3-heptene. A. 2-Butyltriphenylphosphonium Bromide.-.4 pressure hott,le was charged with 78.6 g. (0.30 mole) of triphenylphosphorus,'O 43.8 g. (0.32 mole) of 2-bromobutane and 75 ml. of dry benzene. The bottle and contents were heated a t 140" with shaking for 16 hr., whereupon the bottle was cooled and the supernatant liquid poured away from the amorphous material. The solid was triturated several times with benzene and recrystallized from isopropyl ether-absolute ethanol solvent pair. After drying in vacuo over phosphorus pentoxide, 60.0 g. (50% yield) of a white crystalline solid, m.p. 225-227', was obtained. Anal. Calcd. for CZ2Hz4PBr:C, 66.2; H , 6.1; P , 7.8. Found: C, 66.0; H , 6.4; P , 7.8. B. 3-Methyl-3-heptene.-This olefin, b.p. 119-120' (1it.,ls b.p. 121'); n23~1.4201 (lit.,13 n Z 31.418), ~ was obtained in 66% yield14 via condensation of the phosphorane derived from %butyltriphenylphosphonium bromide with n-butyraldehyde. Anal. Calcd. for C8H16: C, 85.63; H , 14.37. F w n d : C, 85.40; H, 14.70. The product exhibited characteristic infrared absorption bands8 a t 1660 and 836 cm.-l. G.1.c. analysisI2 showed only a single, broad peak. 1-Phenyl-1-butene .-1 -Phenyl-1-butene; b .p. cis, 84 .O-85 .OD / 23 mm.; trans, 91.0-92.0"/23 mm. (1it.,l6 b.p. cis, 187.1"; trans, 198.7'); 1 2 2 3 ~cis, 1.5282; trans, 1.5428 (1it.,l6 n 2 0 ~ cis, 1.5284; trans, 1.5420), was obtained in 78% yieldI4 (59% trans, 19% cis) via condensation of the phosphorane derived from benzyltriphenylph osphonium chloride3 with propionaldehyde. Anal. Calcd. for C10H12: C, 90.85; H , 9.15. Found: C, 90.60; H , 9.27. Stilbene.3-Stilbene, b.p. cis, 135-136'/10 mm.; m.p. trans, 123-125" and mixed m.p. of 123-125' (lit.,17b.p. cis, 136-137"/10 mm.; m.p. trans, 124'); n251)cis, 1.6204 (lit.,17n z 6cis, ~ 1.6214), was obtained in 78y0yield14(42y0 trans; 36% cis) via condensation of the phosphorane derived from benzyltriphenylphosphonium chloride8 with benzaldehyde. 1,3-Heptadiene. A. From Allyltriphenylphosphonium Bromide.3-The olefin, b.p. 99.0-100.0" (lit.,18 b.p. 100.0"); ~ Z O D 1.4417 (lit.,l*n20~1.4428), was obtained in yield14via condensation of the phosphorane derived from allyltriphenglphosphonium bromide with mbutyraldehyde. Anal. Calcd. for C7HI2: C, 87.42; H, 12.58. F o n d : C, 87.54; H , 12.67. B. From Allyltriphenylphosphonium Chloride. 1. Preparation of Allyltriphenylphosphonium Chloride.-A mixture of 131.O g. (0.5 mole) of triphenylphosphoruslO and 300 ml. of allyl chloride was heated under reflux for 24 hr., a t which time the resulting slurry was cooled, and the solid collected by filtration. The salt, m.p. 225-227", was obtained in 64% yield (108.0 g.) upon subsequent washing with benzene and drying i n vacuo a t 100". Anal. Calcd. for C21H?oPC1: C, 74.4; H, 5.0; P, 9.2. Found: C, 73.9; H, 5.9; P , 8.9. 2 . 1,3-Heptadiene.-The olefin, exhibiting a similar boiling range and refractive index as that prepared in ( A ) , was obtained in 52% yield" via condensation of the phosphorane derived from allyltriphenylphosphonium chloride with n-butyraldehyde. The infrared spectra of products (A) and (B) were mutually superimposable and exhibited characteristic bands8 a t 1650, 1600, 1000,955, and 905 cm.-1. A single peak was observed upon g.1.c. analysislZof each product and quantitative catalytic hydrogenation required twci equivalents cf hydrogen per equivalent of diene. 1,3-Nonadiene. A. From Acrolein.--The olefin, b.p. 72-74"/ 43 mm.; TPD 1.4521, was obtained in 3470 yield via condensation of the phosphorane derived from n-hexyltriphenylphosphonium bromide (vide supra) with acrolein. Anal. Calcd. for C9H16: C, 87.02; H , 12.98. Found: C, 87.00; H , 12.81. B. From n-Hexaldehyde.-The olefin, exhibiting a similar boiling range and refractive index as that prepared in (A), was obtained in 30% yield via condensation of the phosphorane de(16) A . L. Henne and A. H. Matuszak, J . 4 m . Chem. Soc., 66, It349 (1949). (17) See Heilbron, "Dictionary of Organic Compounds," Vol. IV. Oxford University Press, New York, N. Y., 1953, p. 375. (18) "Physical Constants of the Principal Hydrocarbons," 3rd ed., T h e Trxns Company, Kew York, N. Y., 1942, p. 40.

377

rived from allyltriphenylphosphonium bromide3 and n-hexaldehyde. The infrared spectra of products ( A ) and ( R ) were mutually superimposable and exhibited charac:t.cristicbandsDat 1650, 1600, 1000, 955 and 905 cn~:-l. 4 single peak was observed upon g.1.c. :tnalysis'2 of cach product and quantitative catalytic hydrogenation required two equivalents of hydrogen per equivalent of diene. 2-Methyl-1,3-nonadiene. A. From Methacroleh-The olefin, b.p. 74-77"/25 mm.; n20~cis, 1.4510; trans, 1.4600, was obtained in 38y0 yield via condensstion of the phosphorane derived from n-hexyltriphenylphosphonium bromide (vide supra) with methacrcilein. Anal. Calcd. for C10H18: C, 86.88; H, 13.12. Found: (cis) C, 87.18; H, 12.92; (trans) C, 87.12; H, 12.88. B. From n-Hexaldehyde. 1. Preparation of Methallyltriphenylphosphonium Chloride.-The salt, m.p. 210-213", was prepared in 90y0 yield from methallyl chlcride and triphenylphosphoruslo by a prwedure similar to that described previously for the preparation of allyltriphenylphosphonium chlcride. Anal. Calcd. for C22H2PC1: C, 74.9; H , 6.24; P, 8.81; C1, 10.1. Found: C, 74.87; H . 6.17; P , 8.71; C1, 10.29. 2 . 2-Methyl-l,3-nonadiene.-The olefin, exhibiting similar boiling range and refractive indices for c i s and trans isomers t o those prepared in ( A ) , was obtained in 14% yield via condensation of the phosphorane derived from methallyltriphenylphosphonium chloride with n-hexaldehyde. Both ( A ) and (B) could be separated into cis and trans isomers by g.1.c. analysis on diethyleneglycol succinate supported on firebrick.'* The cis isomer exhibited characteristic infrared absorpt,ion bands8 a t 1640, 1600, and 885 cm.-l. The trans isomer exhibited infrared bands a t 1640, 1600, 965, and 885 cm.-l. Quantitative catalytic hydrogenation required approximately two equivalents of hydrogen per equivalent of diene. 1,3,7-Octatriene. A. From 4-Pentenal.-The olefin, b.p. 115-117"; n20~1.4594, was obtained in 19.5Y0 yield via condensation of the phosphorane derived from allyltriphenylphosphonium bromide3 with 4-pentenal.10 Anal. Calcd. for C8H12: C, 88.82; H, 11.18. Found: C, 88.48; H , 11.37. B. From Acrolein. 1. Preparation of 4-Pentenyltriphenylphosphonium Bromide.-The salt, m.p. 134-140", was prepared in 90% yield from l-bromo-4-pentenel0 and triphenylphosphoruslo by a procedure similar to that described previously for the preparation of n-hexyltriphenylphosphonium bromide. Anal. Calcd. for CzrH2,PBr: C, 67.1; H , 5.8; P , 7.6. Found: C,66.6; H , 6.3; P , 7.6. 2. 1,3,7-Octatriene.-The olefin, b.p. 120-122", n Z o1.4604, ~ was obtained in 24% yield via condensation of the phosphorane derived from 4-phentenyltriphenylphosphonium bromide with acrolein. Product ( A ) showed a single peak upon g.1.c. analysis12 and exhibited characteristic infrared absorption bands8 a t 1640, 1600, 1000, and 910 cm.-l. Product (B) showed two peaks of similar area upon g.1.c. analysis in diethyleneglycol succinate, supported on firebrickI2 and exhibited characteristic infrared absorption bands8 a t 1640, 1600, 1000, 965, and 910 cm.-l. Quantitative catalytic hydrogenation required three equivalents of hydrogen per equivalent of triene. 1,3,8-Nonatriene. A. Preparation of 5-Hexenyltriphenylphosphonium Bromide.-The salt, m.p. 165-168", was prepared in 95y0 yield from l-brom0-5-hexene~~ and tiiphenylphosphoruslo by a procedure similar t o that described previously for the preparation of n-hexyltriphenylphosphonium bromide. Anal. Calcd. for C Z ~ H ~ ~ PC, B P67.9; : H, 6.3; P , 7.1. Found: C,67.6; H,6.1; P,7.3. B. 1,3,8-Nonatriene.-The olefin, b.p. 68-69",/43 mm. n% 1.4721, was obtained in 20% yield via condensation of the phosphorane derived from 5-hexenyltriphenylphosphonium brcmide with acrolein. The product showed a single peak upon g.1.c. analysis on diethylene glycol succinate supported on firebrick12 and exhibited characteristic infrared absorption bands8 a t 1640, 1600,1000,950, 910, and 900 cm. -l. Quantitative catalytic hydrogenation required three equivalents of hydrogen per equivalent of triene. 1,3,9,11-Dodecatetraene.A. Preparation of Hexamethylenebis(tripheny1phosphonium Bromide.)--A mixture of 262 g. (1 .O mole) of triphenylphosphorus and 122 g. (0.5 mole) of hexamethylene dibromide was heated under a nitrogen atmosphere t o 200' in an oil bath. The wet paste first formed into a viscous liquid and then quite suddenly solidified at 150". The resulting salt wns

HAUSER, BROOKS, MILES,RAYMOND, AND BUTLER

378

allowed to cool t o room temperature and then dissolved in hot chloroform. The product was precipitated by pouring the chloroform solution into 1.5 volumes of acetone, whereupon the solid was collected by f i l b t i o n and dried overnight a t 60' and 40 mm. pressure. A yield of 820/, (297 g.) of the diphosphonium salt, m.p. 335-337", was obtained. Anal. Calcd. for C42H4zPzBrz: C, 65.7; H, 5.5; P, 8.1; Br, 20.8. Found: C, 65.55; H, 5.73; P, 8.18; Br, 20.59. B. 1,3,9,1l-Dodecatetraene.-To a stirred suspension of 76.8 g. (0.1 mole) of hexamethylene bis(tripheny1phosphonium bromide) in 700 ml. of dry ether under a nitrogen atmosphere was added 140 ml. of 14.90y0 n-butyllithium (0.22 mole) in hexane.11 The resulting mixture was cooled to 5' in a Dry Iceacetone bath and a solution of 35 ml. of acrolein in 200 ml. of dry ether was added over a 15-min. period while maintaining the bath temperature a t 5". The reaction was subsequently worked up in a manner similar to that described previously for the preparation of 2octene The olefin, b.p. 71-73'12 mm., n190 1.5093, was obtained in 6% yield.14 The yield could be elevated to 12% of theoretical by use of dielvme as solvent. Aiai. Calcd. for C12H18: C, 88.80; H, 11.10. Found: C, 88.64; H, 11.13. Quantitative catalytic hydrogenation required four equivalents of hydrogen per equivalent of tetraene. 1,3,6&Nonatetraene .-The olefin, b .p. 52 "/20 mm., n * 9 ~ 1.5133, was obtained in 6% yield (12yc yield in diglyme solvent) via condensation of the biphosphorane derived from tetramethylenebis(tripheny1phosphonium bromide)1° with acrolein by a procedure similar t o that described previously fcr preparation of 1,3,9,1l-dodecatetraene. Anal. Calcd. for C9H12: C, 90.00; H , 10.00. Found: C, 89.76; H, 10.40. The product showed a single peak with a shoulder upon g.1.c. analysis in diethyleneglycol succinate supported on firebrick12 and exhibited characteristic infrared absorption bands7 a t 1640, 1590, 1000, and 900 cm. -l. Quantitative catalytic hydroqenation required four equivalents of hydrogen per equivalent of tetraene. Styrene. Procedure A: With Gaseous Formaldehyde.-A 2-1. flask and a 200-ml. flask were connected by means of a wide bore neoprene tube and the 200-ml. flask connected to a suitable nitrogen source. After flushing the entire system with nitrogen, the smaller flask was charged with 20 g. (0.66 equivalent of formaldehyde) of paraformaldehyde (dried in vacuo over phosphorus pentoxide). The larger flask was charged with a mixtuie of 43.3 g. (0.1 mole) of benzyltriphenylphosphonium bromide20and 400 ml. of dry ethyl ether, to the stirred suspension of which was added 80 ml. of 14.90% n-butyllithium (0.13 mole) in hexane" by means of a hypodermic syiinge and a syringe cap. The resulting brilliant orange suspension was allowed t o stir for 0.5 hr., whereupon the smaller flask and contents were heated over a low flame to allow an even stream of formaldehyde and nitrogen to flow over the stirred phosphorane suspension until complete discoloration had been achieved (approximately 15 min.). The reaction was subsequently quenched by the addition of 250 ml. of water t o the heavy, cream-coloied suspension, at which time the layers were separated and the water layer extracted once with 150 ml. of ether. The ethereal extracts were combined, dried over anhydrous sodium sulfate and most of the solvent distilled after removal of the drying agent. The resulting oil was fractionated through a twenty-eight theoretical plates spinning band distillation column (hydroquinone used as inhibitor), after which the distillation fractions were analyzed for yield by g.1.c. analysis on diethyleneglycol succinate supported on firebrick.I2 Styrene, b.p. 52-53'/ 27 mm. (lit.,21 b.p. 52-53"/28 mm.); n'% 1.5461 (lit.,8 n% 1.5462), was obtained in 64% yield14 (6.65 g.). Procedure B: With Paraformaldehyde.-A 0.1 M suspension of benzylidenetriphenylphosphorane was prepared by a procedure similar to that described in (A). However, 6.0 g. (0.2 equivalent of formaldehyde) of dry paraformaldehyde supported in 100 ml. of dry ether was added directly to the stirred suspension, whereupon discoloration was complete within 3.5 hr. a t room temperature. Subsequent work-up of the reaction afforded styrene in 65% yield.]' A similar reaction between the phosphorane derived from beneyltriphenylphosphonium chloride3 and paraformaldehyde

.

(19) G. Wittig, H. Epgers, and P. Duffner, Ann., 619, 10 (1958). (20) G. Wittig and W. Haag, Be?., 58, 1654 (1955). (21) See Heilbron, "Dictionary of Organic Compounds," Vol. IV, Oxford University Press, New York, N. Y., 1958, p. 379.

VOL.28

afforded styrene in 75% yield.14 The phosphorane suspension in this case was completely decolorized within 30 min. a t room temperature. The infrared spectra of ( A ) and (B) were mutually superimposable and each superimposable upon the spectrum of an authentic styrene sample. Qualitative Rate Studies of Betaine Formation as a Function of the Phosphoranes Derived from Benzyltriphenylphosphonium Chloride us. Bromide. A. From Benzyltriphenylphosphonium Chloride.-A300-m1. three-neck flask was placed in a water bath a t 34" and was fitted with a mechanical stirrer, an efficient reflux condenser capped with a calcium chloride drying tube, and a syringe cap. The benzylidenetriphenylphosphorane was formed by reaction of 7.76 g. (0.02 mole) of benzyltriphenylphosphonium chloride3 in 80 ml. of dry ether with 18 ml. of 14.90y0 n-butyllithium (0.03 mole) in hexane" under a nitrogen atmosphere. Dry paraformaldehyde (1.2 g., 0.04 equivalent of formaldehyde) in 20 ml. of dry ether was added to the stirred phosphorane suspension and the resulting mixture allowed t o stir a t 34' until complete decoloiization had been achieved. The styrene product was worked up by a procedure similar to that given previously for pieparation of styrene from paraformaldehyde and analyzed for yield by quantitative g.1.c. analysis on diethyleneglycol succinate supported on firebrick .I2 B. From Benzyltriphenylphosphonium Bromide .-The reactions were carried out in a manner similar t o that described in (A), with the exception that 8.66 g. (0.02 mole) of benzyltriphenylphosphonium bromide20was used. Each of the reactions in (A) and (B) were repeated twice and the results are presented in Table IV. The following six mono- and diterminal olefins were prepaied by similar procedures to those described in either procedure A or B for the synthesis of styrene, with the exception that different phcsphonium salts were employed for each olefin. I-Heptene.-The olefin, b.p. 92-93' (lit.,22 93.6'); n a 0 ~ I .4013 n% 1.3998), was obtained in 47yo yield14 via condensation of the phosphorane derived from n-hexyltriphenylphosphonium bromide (vide supra) with gaseous formaldehyde (see Styrene; procedure A). The infrared spectrum correlated well with a spectrum of 1-hexene as shown in the 1iterature.lS 1-Octene. A. n-Heptyltriphenylphosphonium Bromide.The phosphonium salt, m.p. 171-174", was prepaied in 74% yield from 1-bromoheptane and triphenylphosphorus by a prccedure sjmilar to that described previously for the preparation of n-hexyltriphenylphosphonium bromide with the exception that xylene, instead of monochlorobenzene, was used as solvent. Anal. Caled. for C26HSaPBr: C, 68.0; H , 6.9; P, 7.0. Found: C, 68.0; H , 6.8; P, 7.3. B. 1-0ctene.-The olefin, b.p. 121-122" (lit.,z2b.p. 121.3'); n2% 1.4090 (lit.,22 122% 1.4087), was obtained in 42% yield14via condensation of the phosphcrane derived from n-heptyltriphenylphosphonium bromide with paraformaldehyde (see Styrene; procedure B). Anal. Calcd. for C8Hle: C, 85.62; H , 14.37. Found: C, 85.53; H , 14.53. The decolorization time was normally between 10-12 hr. a t room temperatiire. The infrared spectrum correlated well with a spectrum of 1-octene as shown in the 1 i t e r a t ~ r e . l ~ 2-Methyl-1-Octene. A. 2-OctyltriphenylphosphoniumBromide.-The phosphonium salt was prepared in 66% yield from 2-bromooctane and triphenylphosphorus in a pressure bottle by a procedure similar to that described previously for the preparation of 2-butyltriphenylphosphonium bromide. Anal. Calcd. for C2CHSZPBr: C, 68.6; H , 7.1; P, 6.8. Found: C,68.6; H,7.6; P , 6 . l . B. 2-Methyl-l-octene.-The olefin, b.p. 143.0-144.0", nz0D 1.4197; (lit.,*4 b.p. 143', 71% 1.4190), was obtained in 52% yield14 via condensation of the phosphorane derived from 2octyltriphenylphosphonium bromide with paraformaldehyde (see Styrene; procedure B). Anal. Calcd. for CsHls: C, 85.63; H , 14.37. Found: C, 85.81; H, 14.23. The olefin exhibited characteristic infrared absorption bands8 a t 3075,1665,1375, and 885 cm.-l. lf6-Heptadiene. A. Pentamethylenebis( triph enylphosphonium Bromide).-A mixture of 104.8 g. (0.4 mole) of triphenyl(22) Ref. 13, p. 52. (23) "Infrared Bpectral Data," compiled by the American Pttroleum Institute Research Project 44, Carnegie Institute of Technology, Pittsburgh, Pa., October 31, 19130. (24) Ref. 18, p. 29.

~DIKETONES. IV

FEBRUARY, 1963

phosphorus, 46.0 g. (0.2 mole) of 1,5-dibromopentane and 250 ml. of dry dimethylformamide was refluxed with stirring under a nitrogen atmosphere for 16 hr., a t which time about 130 ml. of solvent was removed by distillation. The residue was allowed t o cool and then poured into 500 ml. of dry benzene. The supernatant liquid was poured away from the resulting pasty material and an additional 200 ml. of dry benzene added t o the paste whereupon immediate crystallization of the product occuired. The solid was broken up and, after washing on the filter utth dry benzene and dry ether, was recrystallized from ethanol-isopropyl ether solvent pair to yield 100 gm. (66% yield) of the diphosphonium salt of m.p. 240-244'. Anal. Calcd. for CaH4&Brz: C, 65.26; H, 5.34; P, 8.21. Found: C, 65.41; H, 5.38; P, 7.83. B. 1,6-Heptadiene.-The olefin, b.p. 89-90", n l * ~1.4151 (lit.,Z4 b.p. 90°, 1 2 2 0 ~ 1.4142), was obtained in 45y0 yield14via

p-Diketones.

IV.

379

condensation of pentamethylenebis(tripheny1phosphonium bromide) with formaldehyde (see Styrene; procedure A). The diene exhibited characteristic infrared absorption bands8 a t 1640,990, and 910 crn.-'. p-Diviny1benzene.-The olefin, b.p. 62-63'/6 mm. (lit.,*& 8586"/16 mm.), was obtained in 42% yield via condensation of the diphosphorane derived from p-xylenebis(tripheny1phosphonium chloride)26and paraformaldehyde (see Styrene: procedure B). Anal. Calcd. for CloHlo: C, 92.26; H, 7.74. Found: C, 91.92; H, 8.02. The diene exhibited characteristic infrared absorption bands8 a t 1625,980, and 900 cm.-l. (25) Lespieau a n d Deliichat, Compt. rend., 190, 683 (1930). (26) T. W. Campbell and R. N. McDonald, J. Org. Chem., 24, 1246 (1959).

Synthesis of Monosubsti t u ted Benzoyl cyclopentanones R. D. C . 4 M P B E L L

AXD

IT.L. HL4R;MER2

Chewiistry Department, State University of Zowa, Zowa City, Zowa

Received October 22, 1962 A series of seventeen monosubstituted benzoylcyclopentanones has been prepared by condensation of the pyrrolidene-enamine of cyclopentanone with substituted benzoyl chlorides. The yields ranged from 28 to 76%. I n some cases, the 2,5-dibenzoylcyclopentanone was isolated. Other methods of condensation of cyclopentanone with benzoate esters were studied; larger amounts of by-products and lower yields of benzoylcyclopentanones resulted. Keto-enol equilibrium data are presented and discussed.

rather than I. The direct benzoylation of cyclopentanone by benzoyl chloride in the presence of sodium amide was reported9 to give I in 53% yield. When p-methoxybenzoyl chloride was used only a 22% yield of the diketone was formed. Self-condensation of cyclopentanone was found to occur under the reaction conditions, decreasing the yield of diketone. When methyl benzoate was employed, no diketone I was 0 11 C . 0 H 6 6 4 formed, and complete self-condensation occurred. l o The synthetic method which we found to be useful Ce"C(CH&COzC2H5 -+ in the series of monosubstituted benzoylcyclopentanones was the condensation of X-cyclopentenylpyrroliI dene withbenzoyl chloride or its monosubstituted derivaThe reaction of 2-cyanocyclopentanone with phenyltives. Stork" reported the preparation of 2-benzoylmagnesium bromide gave a product, m.p. 1 1 7 O , errocyclohexanone by this method, but no conditions or neously identified7 as I. The product melting a t llioyield were given. EistertI2 reported the synthesis of I in 42Oj, yield employing K-cyclopentenylmorpholine. l3 &CN &8-CsH5 0 NH This method was found suitable for benzoylcyclanones of larger ring size.12 CdI5MgBr + We found it possible to prepare monosubstituted benzoylcyclopentanones in satisfactory yields, by use A of the Stork enamine method." Seventeen comhas since been showns to be the imine intermediate pounds prepared this way are listed in Table I with (structure A). Hydrolysis of A gives ring opening, pertinent data. The reaction procedure was essentially that used by others.11-13 The intermediate amino ketone was not isolated. It was hydrolyzed immedi0 H ! ately to give the substituted benzoylcyclopentanone (I-XVII). The diketone resulting from hydrolysis was isolated by three different procedures. Diketones, I, XIII, and XVII, were obtained in sufficient purity by distill(1) Previous paper in this series, R. D. Campbell a n d H. M. Gilow, J. Am. Chem. Soc., 84, 1440 (1962). Taken in part f r o m the M.S. thesis of ing the ether extract of the hydrolysis mixture (proW. L. H.. 1962. In a continuing s t ~ d y ' ~of3 ~benzoylcyclanones ~ it was desirous to prepare a number of monosubstituted benzoycylopentanones. The parent compound 2-benzoylcyclopentanone (I) was first prepared5 by Bauer, in a Dieckmann ring closure, employing sodium amide as catalyst. Sodium ethoxide has also been used.6 The diketone I was reported5p6to melt a t 41-42'.

-

R

Presented in part a t the 141st Kational Meeting of t h e American Chemical Society, Washington, D.C., 1962. (2) hlonsanto Research Fellow, Summer Session, 1961. (3) R. D. Campbell a n d H. M. Gilow, J . Am. Chem. Soc., 82,2389 (1960). (4) R. D. Campbell a n d €1. M. Gilow. ibad., 82, 5426 (19GO). ( 5 ) E. Bauer, Ann. Chzm. Phys., 9,1,393 (1914). ( 6 ) 8. Grateau. Compt. rend., 191, 947 (1930). (7) 0. Riobe a n d L. Gouin, rbid., 234, 1889 (19.52). (8) B. Eistert a n d H. Wurzler, Ann., 660, 157 (1961).

(9) B. 0. Linn a n d C. R. Hauser, J . Am. Chem. SOC., 78, 6066 (1956). (10) C . R. Hauser. B. I. Ringler, F. W. Swamer, a n d W. F. Thompson, ibid., 69, 2649 (1947). (11) G. N. Stork, R. Terrell, and J. Szmuszkovicz, ibid., 76, 2029 (1954); 8ee also Chem. Abstr., 61, 9703e (1957). (12) B. Eistert, W. Reiss, a n d H. Wurzler, Ann., 660, 133 (1961). (13) S. Hiinig a n d W. Lendle, Ber., 93, 909 (1960).